High-molecular polyamide

ABSTRACT

The invention relates to a process for preparing a high-molecular polyamide or polyester by melt-mixing polyamide or polyester having a lower molecular weight with a carbonyl bislactam having formula 1, in which n=an integer of between 3 and 15.  
     With the process according to the invention a permanent increase in the molecular weight of a polyamide is obtained within 2 minutes, whereas this takes at least 10 minutes under comparable conditions using a bislactam according to the state of the art.

[0001] The invention relates to a process for preparing a high-molecularpolyamide, polyester or polyester-amide block copolymer by melt-mixingpolyamide or a polyester or a mixture of a polyamide and a polyesterhaving a lower molecular weight with a bislactam.

[0002] Such a process is for example known from EP-A-0288253, in which,as in other publications, use is made of bis-N-acyl lactams having theformula:

[0003] in which A=alkyl or an aromatic group and n is generally between3 and 11.

[0004] The bis-N-acyl lactams used in the examples are generally tere-or isophthaloyl bislaurocaprolactam or biscaprolactam.

[0005] These bis-N-acyl lactams however have the drawback of arelatively low reaction rate, as a result of which long reaction timesare required to realize the desired increase in molecular weight, whichmay lead to undesired side-reactions, e.g. discolouration of thepolyamide or polyester.

[0006] In practice, bisoxazolines or bisoxazines are therefore morepreferably used as chain extenders for polyamides. The drawback of theseis however that they react with the polyamide's carboxylic end groups,as a result of which the polyamide obtained contains excess amino endgroups and the polyester excess hydroxyl endgroups, which adverselyaffects the thermal oxidative stability.

[0007] The invention's aim is hence a process in which a bifunctionalchain extender that does not involve the above drawbacks is added to apolyamide or a polyester melt.

[0008] The inventors have now most surprisingly found that when thepolyamide or the polyester having the lower molecular weight reacts inthe melt with a carbonyl bislactam, a colourless, stable polyamide orpolyester with increased molecular weight is very quickly obtained.

[0009] ‘Carbonyl bislactam’ is understood to be a compound having theformula:

[0010] in which n is an integer of between 3 and 15. Preferably n=5 to12.

[0011] The carbonyl bislactam can be obtained in a simple manner throughreaction of the lactam with phosgene, COCl₂. The preparation ofN,N′-carbonyl biscaprolactam via this route in benzene in the presenceof a tertiary alkylamine as a catalyst is for example described inJP-A-42017832.

[0012] The amount of carbonyl bislactam used in the process according tothe invention may vary within a wide range. Usually at least about 0.1wt. %, relative to the polyamide or the polyester, will be required toobtain an appreciable effect. Amounts of more than 4 wt. % do notusually lead to a further increase in the molecular weight.

[0013] Usually a person skilled in the art will adjust the amount ofcarbonyl bislactam to be used to the number of amino or hydroxyl endgroups available and the increase in viscosity to be realized as aresult of the increased molecular weight. He will usually determine theoptimum amount for his situation through simple experimentation.

[0014] In principle, the process of the invention can be used for alltypes of polyamides and polyesters. The polyamides include at least thealiphatic polyamides, for example polyamide-4, polyamide-6, polyamide-8etc., polyamide-4,6, polyamide-6,6, polyamide-6,10, etc., polyamidesderived from an aliphatic diamine and an aromatic dicarboxylic acid, forexample polyamide-4,T, polyamide-6,T, polyamide-4,I, etc., in which Tstands for terephthalate and I for isophthalate, copolyamides of linearpolyamides and copolyamides of an aliphatic and a partially aromaticpolyamide, for example 6/6,T, 6/6,6/6,T, etc. The process isparticularly advantageous in the case of partially aromatic polyamidesand copolyamides that require in general a relatively longpolymerisation time.

[0015] The polyesters include at least polyesters derived from aliphaticdicarboxylic acids and dials, polyesters from aliphatic dials andaromatic dicarboxylic acids, copolyesters that are partially aliphaticand partially aromatic and polyesters that contain units derived fromcycloaliphatic dicarboxylic acids. Specific examples are polybutyleenadipaat, polyethyleen terephtalate, polyethyleen naphtalate,polybutyleenterephtalate, copolyesters of polybutyleenadipate andpolybutyleenterephtalate, the polyester derived from butanediol andcyclohexane dicarboxylic acid.

[0016] The process according to the invention can be carried out in asimple manner using the usual melt-mixing techniques and equipment, forexample by dry blending the polyamide or polyester having a lowermolecular weight and the bislactam and optionally also other additivesin a solid state, for example in a tumbler drier, after which themixture obtained is melted in a usual melt-mixing apparatus, for examplea Haake kneader, a Brabender mixer or a single- or double-screwextruder. The different components can also be fed to the mixingapparatus separately.

[0017] Best results are obtained if the lower molecular polyamide orpolyester are thoroughly dried.

[0018] Preferably the carbonyl bislactam is added to the meltedpolyamide or polyester product stream in the polymerisation process asit leaves the polymerisation reactor. The polymerisation process can becarried out both batchwise or in a continuous mode. In the first case areduction of the residence time in the reactor can be realized and thusan increase in productivity; with the continuous process theafter-condensation step, that is necessary usually to obtain a polyamideor polyester of sufficient molecular weight can be avoided.

[0019] The invention will now be elucidated with reference to thefollowing examples, without however being limited thereto.

[0020] Materials used

[0021] a.1. polyamide-6 having a η_(rel)=2.56 measured in formic acidand a concentration of end groups —COOH=0.052 meq/g —NH₂=0.052 meq/g.

[0022] a.2. polyethylene terephtalate, PET, having a η_(rel)=1,44,measured in m-cresol

[0023] b.1. carbonyl biscaprolactam (CBC); from Isochem, France.

[0024] b.2. N,N′-isophthaloyl biscaprolactam (IBC): from DSM RIM NYLON,the Netherlands.

[0025] c. 1,3 phenylene bisoxazoline (1.3 PBO): from Takeda Chemicals,Japan.

[0026] Process

[0027] The polyamide was melted in a Brabender mixer, type Plasticorder651, at 240° C. until a constant torque of the kneaders was obtained,after which the bislactam was added and the mixing was continued. Thekneaders' torque was measured at different times. The mixing was carriedout at a rotational speed of the kneaders of 30 rotations per minute,under a nitrogen blanket to prevent the risk of the polyamidedecomposing as a result of oxidation.

[0028] Table 1 shows the compositions investigated and the results ofthe measurements.

[0029] The results of Experiments 2 vs. 4 show the surprisingly highactivity of the carbonyl lactam, as a result of which a stable highvalue of the melt viscosity (expressed as the Brabender mixer's momentof couple was obtained after 2 minutes already, whereas this is not thecase when use is made of the bislactam according to the state of theart.

[0030] Thanks to this short reaction time, which is of the same order asthe residence time in a normal extrusion, a stable, increased meltviscosity can be realized in practice, and the molecular weight ofpolyamide can be increased, using only a bislactam.

[0031] The relative viscosity, measured in a solution of 1 gram in 100ml of 90 wt. % formic acid, shows the same development as the measuredmoments of couple after 10 minutes. TABLE 1 Experiment 1 2 3 4 5 6Composition (parts by weight) a.1. 100 100 100 100 100 100 b.1. *) CBC0.666 0.666 b.2. *) IBC 0.940 0.940 C. *) PBO 0.570 0.570 0.570 Kneadercouple-moment (Nm)  2 min. 6.0 9.5 10.5 7.0 6.0 8.4  4 min. 6.0 9.5 13.57.2 7.5 10.5  6 min. 6.0 9.5 16.5 8.5 8.5 11.5 10 min. 6.0 9.5 19.5 8.410.5 13.0 relative viscosity 2.6 2.9 3.9 2.7 2.9 3.2 (10 min.) in formicacid

[0032] The process of the foregoing experiments was repeated howeverwith polyethylene terephtalate having a solution viscosity of 1.44 inm-cresol. The temperature was set at 280° C. Compositions and resultsare given in Table 2. TABLE 2 Experiments 7 8 9 10 11 12 Composition(parts by weight) a.2. 100 100 100 100 100 100 b.1. CBC **) 0.96 0.96b.2. IBC **) 1.35 1.35 c. PBO **) 0.27 0.27 0.27 Kneader couplemoment(Nm)  2 min. 0.5 1.0 1.5 1.5 2.0 1.5  4 min. 0.5 1.0 2.0 2.0 2.5 2.0  6min. 0.5 1.0 2.5 2.0 3.5 2.5 10 min. 0.5 1.0 2.5 2.5 4.5 2.5 relativeviscosity 1.44 1.47 1.62 1.62 1.68 1.64 (10 min.) in m-cresol 1 wt. %,135° C.

[0033] Analysis of the endgroups after 10 minutes meltmixing reveals forthe compositions the following data: TABLE 3 COOH— OH— Experiment[meq/gram] [meq/gram]  7 0.041 0.083  8 0.026 0.085  9 0.046 0.031 100.029 0.047 11 0.027 0.028 12 0.018 0.045

[0034] Apparently the carboxy biscaprolactam (CBC) is also reactive withthe carboxyl endgroups. IBC reacts with the hydroxyl end groups only,and seems to be more effective. However also IBC shows to be effectivefor 50% only. For this reason the added quantities IBC and CBC wereincreased in a further experiment by 50%. Very surprisingly in this caseCBC showed much more effectivity than IBC.

[0035] Results are given in Table 4. TABLE 4 —COOH Experiment meq/gramη_(rel) remarks  7 0.041 1.44  9 *) 0.045 1.63 13 0.045 1.69 2.03 pbwIBC 10 *) 0.028 1.65 14 0.021 1.77 1.44 pbw CBC

[0036] Therefore CBC is used in polyesters preferably in excess of theequivalent quantity calculated on the basis of hydroxyl endgroupsavailable in the lower molecular polyester of which the molecular weightshould be increased.

[0037] The molecular weight of the polyamide or polyester having thelower molecular weight may vary over a wide range and is mainlydetermined by economical reasons and the source of the material. Ingeneral it may vary from about 1000 to about 20,000 expressed as numberaveraged molecular weight Mn. However situations are possible in which amixture containing a polyamide or polyester of high molecular weight forinstance 25,000 and an appreciable fraction oligomeric polyamide orpolyester of molecular weight less than 1000 is reacted in the melt withthe CBC according to the present invention.

[0038] The molecular weight of the high molecular weight polyamide orpolyester to be produced by the process of the invention can be freelychosen and generally is higher than 15,000, preferably higher than20,000, even more preferably higher than 25,000.

[0039] The polyamide or polyester obtained by the process of theinvention can be processed by injection moulding, extrusion or blowmoulding to obtain moulded articles, and by melt spinning to obtainfibres.

1. A process for increasing the molecular weight of a polyester, acopolyester, a polyamide, a copolyamide or mixture thereof comprisingmelt mixing the polyester, copolyester, polyamide, copolyamide ormixture thereof with a bislactam and a bisoxazoline, wherein thebislactam is a carbonyl bislactam represented by the following formula:

in which n represents an integer of between 3 and
 15. 2. The processaccording to claim 1, wherein the bisoxazoline is phenylenebisoxazoline.
 3. The process according to claim 1, wherein thebisoxazoline is 1,3 phenylene bisoxazoline.
 4. The process according toclaim 1, wherein n represents an integer of 5 to
 12. 5. The processaccording to claim 1, wherein n represents an integer of
 5. 6. Theprocess according to claim 1, wherein the polyester, copolyester,polyamide, copolyamide or mixtures thereof is melt mixed with 0.1 to 4wt. % of the bislactam, relative to the polyester, polyamide or mixturethereof.
 7. The process according to claim 1, for increasing themolecular weight of a polyamide, wherein the polyamide comprises analiphatic polyamide, aliphatic/aromatic polyamide and/or copolyamide oflinear/aromatic polyamides.
 8. The process according to claim 1, forincreasing the molecular weight of a polyester, wherein the polyester isderived from an aliphatic diol, an aromatic dicarboxylic acid or acycloaliphatic dicarboxylic acid.
 9. The process of claim 1, wherein theprocess further comprises dry blending the copolyester, polyamide,copolyamide or mixture thereof with the bislactam and/or thebisoxazoline prior to melt mixing.
 10. The process of claim 1, whereinthe melt mixing is conducted in a reactor and the bislactam and/orbisoxazoline are added to the copolyester, a polyamide, a copolyamide ormixture thereof exiting the reactor.